Buoywatch
The definition
NOAA defines significant wave height as “the average of the highest one-third of all of the wave heights” measured during the buoy’s roughly 20-minute sampling period. Modern buoys calculate it from the energy in the measured wave spectrum, which gives practically the same value. It was chosen because it matches what an experienced observer estimates when they look at the sea.
Bigger waves do come through
Waves in a sea state vary. According to the US National Weather Service, about 15% of waves will equal or exceed the significant wave height, the highest 10% could be 25–30% higher, and about once an hour you can expect a wave nearly twice the significant height. Some buoys, including Queensland’s, also report the maximum wave in each record.
| If the buoy reads | Highest 10% of waves | Occasional biggest wave |
|---|---|---|
| 1.0 m | about 1.25–1.3 m | up to nearly 2 m |
| 2.0 m | about 2.5–2.6 m | up to nearly 4 m |
| 3.0 m | about 3.75–3.9 m | up to nearly 6 m |
Based on the National Weather Service ratios; real seas vary.
From the buoy to the beach
Offshore buoys measure deep-water waves. As swell reaches shallower water it slows and grows taller before breaking, and long-period swell grows more. Headlands, reefs and sandbanks can focus or spread the energy. So a buoy reading tells you what is coming, not exactly how big it will be at your spot. Period matters a lot here; see Wave Period Explained.
Units and surf scales
Buoys report height in metres; Buoywatch can show feet instead with the units setting on each station page. Surfers in some places use their own scales, which can read much smaller than the buoy, so compare like with like.
Check a live example on the Waimea Bay buoy or the Torrey Pines Outer buoy near San Diego, or find a buoy near you in the buoy directory.
